Set includes: ORVIBO Hubs x 2 ORVIBO Temperature and Humidity Sensors x 2 ORVIBO Gas Detection Sensor x 1 ORVIBO Formaldehyde Detection Sensor x 1 Please refer to the photos for the number of main units and accessories. They were functioning normally until removal, but generally show considerable signs of use. They were used for about 2 years. Please understand that these are used items.